OGC Testbed-13: Geospatial Taxonomies ER

The following requirements are to be addressed in this ER:

The topic of geosemantics and taxonomies for aviation has been explored previously in OGC Testbed 12 (OGC 16-039) and in other domains in depth. In past demonstrations, analyses recommended the use of run-time registries and complex use cases for service discovery and data taxonomy/ontology, but this assumes that the information contained within those services incorporate OWS Context Specification and/or Geography Markup Language (GML) such as the Aeronautical Information Exchange Model (AIXM). However, much of the information exchanged within the FAA National Airspace System (NAS) System-Wide Information Management (SWIM) network is made up of various data models which do not conform with OGC OWS Context specifications. For example, the FAA Traffic Flow Management System (TFMS) and SWIM Terminal Data Distribution System (STDDS) data models contain an XML format which contain geography data (e.g., Lat/Lon coordinates) but do not contain OGC OWS Context data elements or GML.

Another observation is that the current FAA SWIM registry is a design-time registry and does not use the OGC Catalog Service for Web (CSW) [OGC 12-168r6]. While this could potentially change with the anticipated release of FAA Common Support Services (CSS) such as CSS-Aeronautical Information Management (AIM), CSs-Weather (Wx), and CSS-Flight Data (FD), the current direction for the FAA NAS Service Registry Repository (NSRR) is to enhance the current registry search capabilities by creating semantic taxonomies which can be used to categorize services for improved service discovery. These services must have a standard taxonomy in order to incorporate geospatial metadata to enable the discovery of geospatial services. One approach is to define and apply commonly accepted terminology through the use of international definitions at the International Civil Aviation Organization (ICAO) level and national definitions at the FAA level, and so on. Through hierarchical categorization, other nation states may also develop their own national or regional level taxonomies which can be mapped to the international taxonomy for commonality across multi-national domains.

The goal of this ER is to formulate a taxonomy that can incorporate geospatial characteristics identified within a data set into the service metadata and integrate it with SDCM to enable geospatial service discovery in the current registry. Future work areas include a proposed concept for a geospatial identification service using WPS to analyze a dataset and identify geographic characteristics according to a set of taxonomy inputs resulting in a metadata document which can be included in SDCM.

This engineering report documents the concepts of geospatial taxonomies that will efficiently support classification of services based on their geospatial characteristics such as geographical coverage for nation states, flight information regions, and airspace classifications. Thus, the considerations include the use of SDCM and required modifications to support taxonomies developed as part of this activity. The chosen working group for review of this ER is the Geosemantics Domain Working Group (DWG). This work may also be applicable to the Aviation DWG which is co-sponsored by the FAA and EUROCONTROL.

The scope of the Geosemantics DWG is any aspect of conceptual modeling and formal representation of geospatial knowledge which advances the geospatial interoperability mission of OGC. A particular focus will be the adoption or development of tools and methods in support of these activities. It is the mission of the Geosemantics DWG to establish an interoperable and actionable semantic framework for representing the geospatial knowledge domains of information communities as well as mediating between them. This ER will address the need for geospatial taxonomies using aviation-specific geographical conventions (i.e., named boundaries). The use of geospatial semantics will enable better descriptions of services, including OGC web services in the FAA’s SWIM registry as well as in OGC catalogue services.

All questions regarding this document should be directed to the editor or the contributors:

The solutions described in this engineering report may provide further insights if implemented as a greater solution for service registries such as the OGC Catalogue Service. Furthermore, implementation of the recommendations for SDCM will provide a path forward for prototyping and implementation of SWIM registries and discovery of services containing geographical characteristics as described by the taxonomies contained herein.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The Open Geospatial Consortium shall not be held responsible for identifying any or all such patent rights.

Recipients of this document are requested to submit, with their comments, notification of any relevant patent claims or other intellectual property rights of which they may be aware that might be infringed by any implementation of the standard set forth in this document, and to provide supporting documentation.

The following requirements are associated with this engineering report

The following sections have been identified as part of the research conducted for this report:

The taxonomies developed for this engineering report activity are recorded in Taxonomies.

The FAA and SESAR have jointly developed several (SCR) semantic artifacts including common taxonomies (http://www.semantics.aero/). These taxonomies include:

As an example, these taxonomies above can be visualized in Figure 1 below.

These taxonomies, written in Web Ontology Language (OWL) and RDF, provide the basis for taxonomy representation for geospatial taxonomies defined in this engineering report.

ICAO classifies airspace in an alphabetical format (e.g., Class A, B, C, D, E, F, & G). These classes are defined based on separation, altitude, ATC services, aircraft speeds, and communication methods. Generally, airspace classifications depend on concepts of aircraft separation, air traffic control clearance, traffic information (aircraft intent and hazards), and flight rules. Figure 2 is an excerpt from the ICAO Annex 11, Appendix 4 which provides a list of defined airspace classifications. It should be noted that not all nations follow the ICAO methodology for airspace classifications.

Airspace classifications in the U.S. use a modified version of the ICAO Airspace classification rules. These classifications often refer to Air Traffic Management flight rules based on an aircraft’s navigational equipage and classified as Instrument Flight Rules (IFR) and Visual Flight Rules (VFR). For VFR flights, navigation must typically remain at a lower altitude and separation and landing maneuvers are made using human visual cues. In IFR operations, aircraft must be equipped with sufficient navigational equipment such as radar, altimeter, etc. such that the pilot can maneuver aircraft and maintain separation from other aircraft using minimal or sometimes no visual cues (e.g. through fog).

Figure 3 provides a visual representation of the types of airspace classifications used in the U.S. [1]:

Figure 4 provides a description for each Airspace class in the U.S.

Source: https://www.faasafety.gov/gslac/ALC/course_content.aspx?cID=42&sID=505&preview=true

Class A Airspace is from 18,000 feet Mean Sea Level (MSL) up to and including Flight Level (FL) 600. This includes airspace up to 12 nautical miles off the coast of the contiguous United States and Alaska. Any space beyond the 12 nautical miles off the coast line is considered international airspace. Domestic radio navigational signal and ATC radar coverage is required to be considered Class A airspace. All aircraft must fly under IFR in Class A airspace.

Class B Airspace is bounded from the surface to 18,000 feet MSL surrounding major airports. The volume of airspace for Class B is designed based on the surface area of the airport and the volume of terminal airspace controlled by the airport or terminal air traffic control center. All aircraft require ATC clearance to operate within this airspace. ATC manages separation of aircraft. VFR operation may be flown if a cloud clearance is provided by ATC. Class B aeronautical charts contain geographical fixes which correlate to appropriate frequencies in which aircraft must obtain ATC clearance before entering the airspace. Currently, 12 airports have Class B airspace. A list of Class B airspaces for FAA based on airports are provided in Airports and Facilities.

Class C Airspace is bounded from the surface of the airport to 4,000 feet MSL. The first layer of the airspace is from the surface area to the ceiling boundary with 5 nautical miles radius. The second layer is from 1,200 feet MSL to the ceiling at a 10-mile radius. The outer layer extends to 20 nautical miles radius. Class C airspace surrounds airports containing regular commercial traffic of 100 passengers per flight or more. Class C airspaces contain an operational tower, radar-controlled approach system, and a minimum number of IFR approaches per year.

Class D Airspace is bounded from the surface of an airport to 2,500 feet MSL. The outer boundary radius varies but is typically 4 nautical miles. Class D airspace is classified as any airport with a functional control tower with minimal IFR approaches. The airspace reverts to Class E or G during hours when the tower is closed or under special conditions.

Class E Airspace is controlled airspace that is neither A, B, C, or D. this airspace extends from 1,200 feet Above Ground Level (AGL) up to 18,000 feet MSL. Some areas as low as 700 AGL are included and are notated in sectional charts. Most of the airspace in the United States is class E.

Class F Airspace is not used in the U.S. ICAO defines Class F airspace as a hybrid of Class E and G airspace in which ATC separation guidance is available but not required for IFR operation.

Class G Airspace includes all airspace below 14,500 feet MSL which is not otherwise classified or controlled. Class G airspace is considered uncontrolled airspace.

Special Activity Airspace (or Special Use Airspace) refers to airspace which can be designated for a given geospatial volume for reasons such as national security, public events, military exercises, etc. SAA can be contained within any given airspace classification above, and should be designated by both with a service taxonomy.

Historically, ICAO led a study to define regional air navigation (RAN) and continued to refine the air navigation regions in 1964 with the Air Navigation Commission. Further consolidation occurred in 1980, and the present regional structure is defined in the Appendix 1 of the ICAO Doc 8144-AN/874: Directives to Regional Air Navigation Meetings and Rules of Procedure for their Conduct. These regions are comprised of the following regions:

A visual depiction of an ICAO Region taxonomy is shown in the Figure 5:

A taxonomy for ICAO Regions is provided in Taxonomies.

Each of the ICAO regions defined above also contain multiple Flight Information Regions defined based on major areas of air traffic control services such as flight information services and alerting services (ALRS). Each ICAO region contains a number of agreed upon FIRs [4]. Each FIR contains an FIR ID annotated using a four letter code. Primarily, the ICAO FIR ID will be used for identifying an ICAO designated FIR. However, when attempting to identify an Area Control Center, a different identification code may be used based on each nation.

In the U.S., Area Control Centers are called Air Route Traffic Control Centers (ARTCC), or simply Centers, which contain ARTCC codes which differ from ICAO FIR IDs. For example, ARTCC ZDC is for the Washington D.C. ARTCC, but the ICAO FIR ID is KZDC. An ARTCC taxonomy would provide value for identifying data which either refers to information contained within an ARTCC, but also for information such as flight plans which either depart or arrive in an ARTCC’s airspace. Taxonomies could be defined based on ARTCC codes, but usage should take into consideration additional taxonomies for usage (e.g., Departures, Arrivals, En Route, etc.) to maximize the relevant discovery of services.

In the U.S., ARTCCs are also further broken down into En Route sectors or oceanic sectors. These are separated based on En Route navigation systems (i.e., En Route Automation Modernization - ERAM), Oceanic navigation systems (i.e., Advanced Technologies & Oceanic Procedures - ATOP), and Terminal Approach. These sectors can also be identified according to the taxonomy structure shown in Figure 6.

Terminal facilities include TRACONs and ATCTs which are located in various airport facilities across the FAA National Airspace System [3]. These terminal facilities can be designated as Class B or Class C airspaces and include Location ID (LocID) per each facility. Due to the long list of facilities, a taxonomy was not generated for this report, however a list of TRACON and ATCT facilities is provided in Airports and Facilities.

Airways in the U.S. were historically identified based on radio frequency. Later, they were based on frequency ground stations such as beacons. Low altitude airways below 18,000 feet are based on VOR stations and appear on published navigational charts. These airways are prefixed with the letter "V" and called "victor airways". High altitude airways from 18,000 feet which are based on VOR stations are called jet routes. They appear on high altitude charts and are prefixed with the letter "J". With the invention of RNAV routes, low altitude routs were prefixed with "T" and high altitude routes were prefixed with "Q". These routes can be identified according to the taxonomy structure shown in Figure 7.

The airspace classifications can be identified based on geospatial boundaries of each airspace as determined by an ATM provider’s definition. These are defined differently per nation, which makes it near impossible to define a single taxonomy definition for every nation state. Therefore, an airspace classification taxonomy should be defined at the ICAO level, and another level of airspace classification needs to be defined at each national level. A reference mapping between the two taxonomies can provide a translation between airspace users trying discover the data services across multiple nation states by searching across airspace classifications.

If a data service provider wishes to annotate their data services with a taxonomy classification based on airspace, their specific nation’s taxonomy structure may be used, provided that a mapping from the national taxonomy to the ICAO taxonomy exists. In this way, a service user may search across a registry through SDCM profiles to discover the services based on a search parameter for the ICAO taxonomy term [2]. Specific geospatial features (e.g. Class B airports) will require identification of the airspaces around those features. For example, a user client may select "all Class B airspaces", in which all airports that fall within the geospatial classification of Class B airspace are associated and provided back to the user.

Based on the aforementioned geospatial classifications defined by ICAO and the U.S., the geospatial taxonomies can be represented as follows:

In Figure 8, each airspace can be categorized by airspace classification. The airspace classifications contain additional information which are documented in individual taxonomy documents attached in Taxonomies. Flight Information Regions are based on the area control centers for the U.S. The airspace volume regions can be identified using FIR ID, ARTCC code, and either enroute, oceanic, or terminal facility code. The airways are identified by instrument flight rule encodings. The combination of these taxonomies should be sufficient to identify data according to the following criteria:

The fourth dimensional component of time is not considered a geospatial taxonomy. However, temporal filters can be applied at the registry level to filter information contained within data based on data timestamps.

Using SDCM and the proposed taxonomies can provide sufficient discoverability for services containing geospatial information which do not conform to the OWS Context or GML. These data services can still be tagged with sufficient metadata to assist users in discovering relevant information for their operation. Additionally, services that do contain geospatially searchable data can still benefit from this method of metadata descriptions by tagging the services with taxonomy values which reflect the geospatial information for users who do not have OWS clients.

An OGC WPS can be used to analyze geospatial data sets which contain geographical identifiers which match taxonomy metadata which can be included in the service description based on a geospatial feature criterion. The criterion can be identified using the taxonomy sets and associated geospatial definitions from authoritative sources. This service could also be executed periodically to determine if a data set changes for automatic updating of registry metadata. Furthermore, such a service could also provide a validation for standard data sets to ensure they are properly described in the registry. For example, in Figure 11, a taxonomy such as US-FIR can be used as an input to the OGC WPS. This taxonomy identifies value pairs such as "KZDC" for an area control center which is semantically linked to an ARTCC facility value in a data set such as in the FAA’s Traffic Flow Management System (TFMS). The TFMS schema contains an element variable which acts as the geographical identifier which, in this case, is the ARTCC facility code. Using the schema and the taxonomy convention, the data of a corresponding data service can be analyzed for any matches between the schema data element and the taxonomy to determine matches. Any matches can be used to generate the service metadata documentation.

Additional schema-specific logic would be required in order to map the Geospatial taxonomy to data to a geographical baseline. For example in the taxonomies provided in Taxonomies, an airspace class taxonomy for airspace class A, B, C, etc. is provided. A baseline geospatial mapping of these airspace volumes could provide a baseline to compare with other geographical data. If geographic information fields (i.e., lat/lon coordinates) in a data service field match geographical markers within the baseline data, the metadata can be assigned based on the taxonomy match and applied to the service metadata. In Figure 12, the addition of geography markers which identify geospatial boundaries can be used to identify geometrical values within data. For example, if the baseline data contains annotated geometry volumes for Class B Airspaces, then in the case of the SWIM Terminal Data Distribution Service (STTDS) which contains airport position reports within terminal airspace, the schema value for the lat/lon coordinates can be compared to the set of geometries to determine if that the data contains matching information. The WPS can then match the geography markers of the baseline data to generate the service metadata documentation.

It can be considered that if an aviation geospatial taxonomy is to be designated for a service registry, and is maintained universally, the authority for determining the taxonomy and related sub-elements within the taxonomy lies on the governing authority. In this case, ICAO already develops and maintains a set of taxonomies for various operations. The ICAO ATM Information Reference Model (AIRM) is a structured, traceable, unified, harmonized, common, digital representation of civil and military information constructs relevant to ATM in support of information exchange via SWIM ^[1]. The ICAO AIRM is based on similar work done by EUROCONTROL ^[2]. In the future, a standard methodology could be developed based on the conceptual model of the AIRM would provide an authoritative source for standardization of service metadata in the Aviation domain.

The following Class B airports are defined for FAA:name: value

Arizona:

California:

Colorado:

Florida:

Georgia:

Hawaii:

Illinois:

Kentucky:

Louisiana:

Maryland:

Massachusetts:

Michigan:

Minnesota:

Missouri:

Nevada:

New Jersey:

New York:

North Carolina:

Ohio:

Pennsylvania:

Tennessee:

Texas:

Utah:

Virginia:

Washington: